Of those reviews, only the techpowerup one lists the power consumption of just the card, the other two list numbers for the whole system. And even those numbers are measured at the socket, so they are 15-20% higher then what the components are pulling from the psu.
Also, those 163W in the techpowerup review are the worst-case scenario, probably running furmark. Mining should use less power as some parts of the gpu are not used at all. And if you downclock the memory (which you should), you save something like 10-20W per card. I'd be surprised if a 6870 at stock gpu clock and downclocked memory uses more than 120W while mining. Overclocking the gpu, without raising the voltage, can push that to maybe 140W. You can reach ~1GHz on the gpu without overvolting.
So the three of them should use some 400W, most of it from the 12V rail. Add max 100W for the rest of the system, so you need a PSU that can output ~40A on the 12V rail. Any quality >=600W PSU should be able to do that, even some 500W might work.